The present invention is directed to imaging apparatuses and processes. More specifically, one embodiment of the present invention is directed to a process wherein a latent ionographic image is formed on an imaging means with a peel layer, the latent image is developed with a developer, and the peel layer containing the developed image is simultaneously removed from the imaging means and transferred to a substrate. In another embodiment, a first latent image may be formed on the peel layer and developed with a first developer of one color, followed by formation of a second latent image on the imaging peel layer and development of the second latent image with a second developer of a color different from that of the first developer, and, if desired, followed by subsequent image formation and development steps to form an image of the desired number of colors, followed by simultaneous removal and transfer of the peel layer containing the developed image from the imaging means to a substrate. Images of two or more colors can thus be formed with the apparatuses and processes of this embodiment of the invention.
Another embodiment of the invention entails formation of a latent image on an imaging means, development of the latent image with a transparent waxy toner, which may be either a liquid toner or a dry toner, to form wax images on the imaging means, subsequently forming a second latent image on the wax images, and developing the second latent image with a colored developer. This process may be repeated by forming a third latent image on the wax images, followed by development of the third latent image with a developer of a color different from that of the first colored developer, followed by repeating the process to form fourth and additional images. The wax images containing the developed images are subsequently simultaneously transferred to and affixed to a substrate.
Another embodiment of the invention entails formation of a first latent image on an imaging means and development of the first latent image with a first liquid developer, followed by formation of a second latent image on the imaging means containing the first developed image and development of the second latent image with a second liquid developer, wherein the liquid medium of the first and second liquid developers comprises a volatile liquid and a nonvolatile liquid, so that subsequent to development, a residual oil film remains between the imaging means and the colored particles of the developer, thereby facilitating transfer of the developed image from the imaging means to the substrate. In this embodiment, the imaging means may optionally bear a peel layer.
Still another embodiment of the present invention entails formation of a latent image on an imaging means and development of the latent image with a liquid developer comprising a liquid medium, toner particles, a waxy release agent, and a charge control agent, followed by repetition of the process to form at least one additional image of a color different from the first image on top of the first image, wherein the waxy component of the liquid developers forms a peel layer between the imaging means and the toned images, thereby facilitating transfer to a substrate. The liquid developers can either contain toner particles and separate transparent particles of the waxy release agent, or they can contain toner particles comprising a colorant and a waxy release agent.
Yet another embodiment of the present invention entails ionographic formation of a latent image on an imaging means, development of the latent image with a dry toner comprising toner particles and a waxy release agent, and affixing of the developed image to the imaging means, followed by repetition of the process to form at least one additional image of a color different from the first image on top of the first image, wherein the waxy component of the dry toners forms a peel layer between the imaging means and the toned images, thereby facilitating transfer to a substrate. The dry toner can either comprise toner particles and separate transparent particles of the waxy release agent, or it can comprise toner particles comprising a colorant and a waxy release agent.
In ionographic imaging processes, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 2,919,171, 4,524,371, 4,619,515, 4,463,363, 4,254,424, 4,538,163, 4,409,604, 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093, the disclosures of each of which are totally incorporated herein by reference. Generally, the process entails application of charge in an image pattern with an ionographic writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
Processes for forming images with dielectric materials are known. For example, U.S. Pat. No. 4,395,472, the disclosure of which is totally incorporated herein by reference, discloses a process for developing monochromatic or polychromatic photographic images directly on plain paper by a photodielectric selective sublimable dye transfer process. A photosensitive belt containing a photodielectric material and a binder is exposed to a light image, and the exposed areas are then passed in contact with a plain paper together with a carrier of sublimable dye under pressure and the application of an electromagnetic field. Multicolor images are formed by exposing the original through three separation filters, such as red, blue, and green, on three succesive areas of the photosensitive belt, and each exposed area is passed in contact with a plain paper and three successive carriers of sublimable dyes of color corresponding to the separation filters. The belt is coated on the outer surface with a photodielectric layer. Suitable binders for the photodielectric compositions include binders of low dielectric losses, such as butadiene, styrene, butadiene copolymers, nylon, silicon resins, and the like.
In addition, U.S. Pat. No. 4,353,970, the disclosure of which is totally incorporated herein by reference, discloses a method and apparatus for charging a dielectric layer electrostatically to a predetermined potential. In various embodiments, the dielectric layer may consist of a photoconductive and/or thermoplastic recording base, during the charging of which at least one of an A.C. or D.C. voltage field is modulated to apply a stream of ions to the charged dielectric layer. Further, U.S. Pat. No. 4,403,848 discloses an electronic color printing system with multiple scanning beams, each modulated in accordance with distinct color image signals. The photoreceptor for the system preferably comprises an inner layer or substrate composed of a suitable flexible electrically conductive substrate with an outer photoconductive layer. The photoreceptor material may further consist of a transparent polymer overcoating containing a charge transport compound. Each color image is developed prior to scanning of the photoreceptor by the next color image signal beam. Following development of the last color image, the composite color image is transferred to a copy sheet. Another method of preparing multicolor images is disclosed in U.S. Pat. No. 4,286,031, the disclosure of which is totally incorporated herein by reference, which discloses a printing method and apparatus in which an elongated substrate such as a strip, fabric, synthetic resin sheeting, foil, or the like is printed with a plurality of patterns from multiple independent color stations to achieve a composite multi-colored image.
Another process for forming full color images is illustrated in Color Xerography With Intermediate Transfer, Xerox Disclosure Journal, Vol. 1, No. 7 (July 1976), which discloses an apparatus having four photoreceptors and corresponding development systems and operates by sequentially forming and developing images on the photoreceptors, followed by transfer of each image in registration with the other images to an intermediate transfer member. The fully formed color image on the transfer member is then transferred to a substrate.
The use of liquid developers in imaging processes is known. For example, U.S. Pat. No. 3,843,538 discloses a developer emulsion comprising a disperse water phase and a continuous phase which is a solution of a pigmented high molecular weight polymer dissolved in an appropriate organic solvent. The emulsion is non-conductive, and may also be stabilized by a surface-active emulsifying agent with a predetermined hydrophilic-lipophilic balance. The liquid component of the emulsion is a solution of polymer resins in an organic solvent of about 90 percent Isopar.RTM. G and 10 percent aromatic hydrocarbons. A release agent, such as polyethylene wax, may be added to assist image transfer. The aqueous component allows for reduction in the amount of isoparaffin solvent which must be evaporated from the photoconductor after transfer. In addition, U.S. Pat. No. 4,659,640, the disclosure of which is totally incorporated herein by reference, discloses a liquid developer containing a volatile liquid carrier, wax, and polyester toner particles. The developer is self-fixing at room temperature as a result of the high wax concentration. Isopar.RTM. G is a preferred liquid carrier, and Epolene is a preferred polyethylene wax.
Further, M. R. Specht, L. Contois and D. Santilli, "Film, Toning Ink and Process in the Kodak Signature Color Proofing System," Third International Congress on Advances in Non-Impact Printing Technologies (Aug. 24-28, 1986) discloses an apparatus that employs a multilayered sheet comprising a 7-mil polyethylene terephthalate film support, a transparent conductive layer, a transparent photoconductor layer, and an overcoat layer. Each transparent original is rear exposed through the transparent layers with UV-blue light and developed with a liquid developer on the overcoat layer. After drying, subsequent color separation images are formed in the same manner directly over the developed image of previously formed color separations. When the complete image is formed, it is transferred with the overcoat layer to coated press stock with a heat/pressure laminator.
Additionally, U.S. Pat. No. 4,725,867 discloses an electrophotographic apparatus for forming a subsequent toner image overlapping one or more toner images previously formed on the surface of an electrophotographic element. The apparatus includes means for electrically charging the surface and the previously formed toner image or images, and means for forming an electrostatic latent image overlapping the previously formed toner image or images on the surface by imagewise exposing the element, through the previously formed toner image or images. The latent image forming means provides actinic radiation of a wavelength outside the range of 400 to 700 nanometers with the density of the previously formed toner image or images to the actinic radiation being less than about 0.2.
Further, U.S. Pat. No. 4,600,669 discloses an electrophotographic proofing element comprising a photoconductive layer on an electrically conducting substrate, capable of transmitting actinic radiation to which the photoconductive layer is responsive, and a dielectric support releasably adhered to the substrate comprising the photoconductive layer or an overcoat thereof forming a surface of the element capable of holding an applied electrostatic charge. To use the element, the surface of the dielectric support is charged and the photoconductive layer is imagewise exposed to actinic radiation, thereby forming a developable electrostatic image on the dielectric surface. The electrostatic image, in turn, is developed with toner to form a first color image. A composite color image is formed on the element by repeating the sequence one or more times with imagewise exposure of the photoconductive layer to actinic radiation transmitted through the transparent support, and developing over each preceding image with a different color toner. The composite toner image is transferred with the dielectric support to a receiving element to form a color copy such as a three-color filter array or a color proof closely simulating the color print expected from a full press run.
In addition, U.S. Pat. No. 4,659,640 discloses a liquid developer containing a volatile, electrically insulating carrier liquid, polyester toner particles, and wax dispersed in the carrier. The wax-to-polyester weight ratio in the developer is sufficiently high to render the developer self-fixing at room temperature. The resulting images developed with the developer become fixed to surfaces without the need for externally applied heat.
Further, U.S. Pat. No. 4,660,059, the disclosure of which is totally incorporated herein by reference, discloses an apparatus in which a document is printed in at least two different colors. Ions are projected onto the surface of a receiving member to record at least two electrostatic latent images thereon. Each of the electrostatic latent images recorded on the receiving member is developed with different color marking particles, and the different color marking particles are transferred substantially simultaneously from the receiving member to the document to print the desired information thereon.
Additionally, U.S. Pat. No. 3,672,887 discloses a process for reproduction of a multicolor original in an electrophotographic development employing superimposed development of multiple electrostatic latent images present on an electrophotographic photosensitive layer which is provided with low photoconductivity for a certain wavelength region, and has increased photoconductivity in at least a part of the remaining wavelength region. At least one development is obtained with a toner having photoconductivity for light of the wavelength region in which the electrophotographic level has low photoconductivity.
Further, U.S. Pat. No. 3,687,661 discloses a color reproducing process in which a series of color toner images are sequentially developed in superposition upon the surface of a photoconductive plate. Between each development step, the plate is imaged by charging the plate to a potential of a first polarity in both the previously developed and non-developed regions. The charge accepted in the previously developed regions is then partially neutralized by applying thereto a second charge having a polarity opposite to that of the initial charge whereby the original charge in the previously developed regions is reduced to a level substantially equal to the potential in the non-developed region. The now uniformly charged plate is exposed to a light image containing additional input scene information relating to the next image to be developed.
Another reference, U.S. Pat. No. 4,497,570, discloses a printing machine having an operator removable housing comprising a photoconductive member with a web entrained about a portion thereof. A latent image is recorded on the photoconductive member and marking particles transported to the portion of the web entrained about the photoconductive menber. In this way, the latent image recorded on the photoconductive member attracts the marking particles to the web in image configuration. A copy sheet is advanced into contact with the marking particles on the web. The marking particles interposed between the web and the copy sheet are heated. After cooling, the copy sheet is separated from the web with the marking particles remaining affixed thereto.
Additionally, U.S. Pat. No. 3,927,934 discloses an electrostatographic reproduction machine having a web cassette which comprises separable portions for feeding a web between the photoreceptive surface and the developer means of the machine to provide a developed image on the web for subsequent transfer to suitable support material.
Further, U.S. Pat. No. 3,937,572 discloses an apparatus for inductive electrophotography in which a thin insulative film is applied to be in direct contact with a surface carrying an electrostatic image which has a potential sufficient for adherence by induction of toner to the insulative film but insufficient to discharge when in contact with or upon separation of the toned insulative film. When the surface is photoconductive, it is exposed before or after contact with the insulative film to a pattern of discharging radiation to form an electrostatic image thereon. As one form of image development, toner is applied to the insulative film while in direct contact with the imaged surface. Thereafter, the toner image may be transferred to a support member. Toning and toner transfer is repeated without further charge and without further exposure.
In addition, U.S. Pat. No. 4,021,106 discloses an electrostatic reproduction process wherein a transparent charged sheet of insulating material, such as a thin insulating film bearing a uniform electrostatic charge on one side thereof, or an electret, is placed against an electrostatically charged photoconductive surface on a suitable substrate to form a temporary composite. The photoconductive surface is then exposed to a light pattern and the free surface of the transfer sheet is developed to provide a visible image corresponding to the light pattern. This image is fixed on the transfer sheet or is transferred to a receiving sheet after the transfer sheet has been removed from the photoconductive surface. Further copies can be made by reapplying the transfer sheet to the photoconductive surface and redeveloping the free surface of the transfer sheet when in place on the photoconductive surface.
In addition, imaging systems such as those disclosed in U.S. Pat. Nos. 4,569,584; 4,485,982; 4,731,622 and 3,701,464, the disclosures of each of which are totally incorporated herein by reference, employ a process wherein color images are formed on top of each other on a dielectric paper.
Liquid developers have many advantages, and often result in images of higher quality than images formed with dry toners. For example, images developed with liquid developers can be made to adhere to paper without a fixing or fusing step, so there is no need to include a resin in the liquid developer for fusing purposes. In addition, the toner particles can be made very small without resulting in problems often associated with small particle powder toners, such as machine dirt which can adversely affect reliability, potential health hazards, limited crushability, and restrictions against the use of coarsely textured papers. Development with liquid developers in full color imaging processes also has many advantages, such as a texturally attractive print because there is substantially no height build-up, whereas full color images developed with dry toners often exhibit height build-up of the image where color areas overlap. In addition, full color imaging with liquid developers is economically attractive, particularly if the liquid vehicle containing the toner particles can be recovered economically and without cross contamination of colorants. Further, full color prints made with liquid developers can be made to a uniformly glossy or a uniformly matte finish, whereas uniformity of finish is difficult to achieve with powder toners because of variations in the toner pile height, the need for thermal fusion, and the like.
When full color images are formed by sequential imaging and development with different colored developers, the ability to maintain consistency of hue in the final image depends, in part, upon achieving good registration of the several primary color images needed to form the composed color. In many printers employing powder toners, the images are formed by formation of the latent image for the first primary color on an imaging member, developing the image, transferring the developed image to a substrate such as paper, and cleaning residual toner from the imaging member, followed by repetition of the process for the second and third primary colors and, optionally, with black, until the complete image is formed. The final image is then fused to the substrate.
In this process, achieving synchronous transfer or registration of the images to the paper, wherein each individual colored image is transferred to the desired position relative to the positions of the other individual colored images, is extremely difficult. The apparatus and process of the present invention provide a means for forming full color images with excellent registration, thus avoiding the difficulties encountered with many prior art processes wherein transfer of each developed image to a substrate occurs prior to formation and development of the next image.
Although known imaging processes are suitable for their intended uses, a need continues to exist for ionographic imaging processes that enable formation of prints of high image quality. A need also exists for ionographic imaging processes which enable formation of full color prints of high image quality and excellent registration. In addition, there is a need for ionographic imaging processes wherein the images formed and developed can be transferred to plain paper with a wide range of textures. There is also a need for ionographic imaging processes wherein full color images are formed with excellent registration. Further, a need exists for ionographic imaging processes wherein full color images are formed and developed with liquid developers, thereby enabling the formation of very high quality images. Additionally, there is a need for ionographic imaging processes wherein the prints formed have a uniformly glossy or uniformly matte finish. There is also a need for economically attractive ionographic imaging processes wherein an image is formed on a dielectric layer and developed with a developer, and the dielectric layer is subsequently transferred and affixed to a substrate. A need also exists for ionographic imaging apparatuses suitable for carrying out the processes of the present invention and having simplified machine architecture.